A true manufacture with 145 years continuous history, including the birth of the El Primero - enough said! Zenith is already everything brands like IWC want to be!
The technical merit of the product is unquestionable and under the new direction, their collections are now very attractive. So many 'big brands' are actually just well marketed brands - for me, Zenith is the opposite - instead of spending millions to get Kevin Spacey to wear their watches, they spend it developing mind blowing complications like the Zero G.
However, if by the 'next big brand' you mean a potential boom and bust, then it could never be a historical brand like Zenith, it would more likely be a trendy brand, but i have no interest in trendy brands!